Oestrogen Reduces Aggression

The identification of cancer stem cells (or tumour-initiating cells) has opened up a new perspective on breast cancer, with new hopes for treatment in the future. To date treatment against cancer was designed to reduce the mass of the tumour. Nevertheless, what has recently been discovered is that, while traditional treatment is capable of killing most of the cell mass of the tumour, the cancer stem cells are more resistant to common treatment such as chemotherapy and radiation. Thus, in order to cure the cancer with greater efficacy and definitively, it is important to find ways to eliminate cancer stem cells as well.

Oestrogen on the one hand is essential for the normal development and functioning of the breast and, on the other, this same hormone induces the proliferation of cancer cells once the breast tumour has appeared, i.e. oestrogen is also a risk factor in breast cancer. However, nothing or little has been known the effect of oestrogen on the tumour-initiating cells.

Over recent years, important steps in the fight against breast cancer have been taken, notable enhancing its diagnosis, prognosis and possible treatment. It had also been proposed that the number of cancerous stem cells is correlated with the aggressiveness of the tumour: The greater the percentage of breast cancer stem cells, the greater the aggressiveness and the worse, thereby, its prognosis.

“To our surprise, what we have seen is that oestrogen reduces the proportion of breast stem cells which means a mechanism for explaining this better prognosis observed with tumours that express the oestrogen receptor. That is, those tumours expressing the oestrogen receptor are less aggressive, better differentiated and thus have a better prognosis”, explained María Vivanco, leader of the research team.

Vivanco believes that this study presents a new functional aspect of oestrogen, due to its capacity for acting in a different way depending on cellular type.

In the opinion of the researcher, the study “has set out the molecular bases for understanding the direct effect of oestrogen on the proportion of stem cells, whether in healthy or cancerous tissue and the fact that the oestrogen receptor is an excellent prognostic marker”.